Sulfur mustard is a continued major military threat, and has grown to become also a chemicalterrorism threat against civilians in post-9/11 era. These threats combined require approaches and strategies for 1) the measurement of injuries, and 2) prophylactic and therapeutic countermeasures. Accordingly, the central focus of this grant is to develop 2-chloroethyl ethyl sulfide (CEES)-induced skin toxicity models, and generate critical pre-clinical efficacy and mechanistic data with silibinin in various cell culture and animal models. The selection of skin toxicity models is based on 1) known skin toxicity of sulfur mustard/CEES, and 2) twenty-five years of the P.I.' research experience with skin diseases research. The selection of silibinin is based on about 2000 years of its history for human usage as an anti-hepatotoxic agent, almost 35 years of its history as a dietary supplement and a clinical therapeutic agent around the world including the United States for liver toxicity, about 15 years of the P.I.' experience with this agent as preventative and therapeutic modalities against various skin disorders induced by toxic chemicals and ultraviolet radiations, and the fact that this agent is in phase II clinical trial for its efficacy against prostate cancer. Specific aims proposed are: 1) Assess CEES-induced biological alterations and associated mechanisms in epidermal keratinocytes in cell culture, and determine whether some biomarkers of CEES-induced injuries could be established. 2) Assess CEES-induced skin tissue injuries and associated mechanisms in mice, and seek whether there are similarities between study outcomes in aims 1 and 2. 3) Assess and establish silibinin efficacy prior and/or after CEES challenge in cell culture models. 4) Assess and establish in vivo efficacy of silibinin on CEES-caused skin toxicities and associated mechanisms in mice; both topical and dietary silibinin treatments will be performed before and/or after CEES challenge. We believe that outcomes of the studies proposed above in four aims would set the stage for moving forward with next step of silibinin efficacy studies in well-identified and established sulfur mustardinduced toxicity models in mice at appropriate facilities. Positive outcomes of those assessments would move this non-toxic, low-cost and well-accepted by humans as dietary supplement agent for human usage against sulfur mustard caused skin and possibly other organ toxicities.